Valve recession rate

[MikeFossl]

After 6 months and 15000 km, it looks as though the exhaust valves recede at about .05 mm per 3000 km.  Intake valves are pretty stable.  Is this excessive?  Checking the valve clearance every 3000 k isn't too much of a chore but at what point will I run out of adjustment?

[montmil]

If memory serves, BMW pretty well eliminated the exhaust valve seat recession issues with the 82/83 product line. Might there be something else going on? Is this occurring on both heads or just one? That much closure in valve lash would have me pulling the heads for inspection.

[Barry]

Apologies for having to convert the metric units before they mean something to me.

 0.002" in under 2000 miles is definitely not normal. And yet your 85 should (just) have received the modified valve seats with improved thermal conductivity that was supposed to solve the valve recession problem that occurred on some 81 - 84 bikes

The way of telling if you have the updated valve seats is there are supposed to be 2 scribed lines on the inside edge of the 85 on valve seats and only one line on the 81 -84 seats.

Another possibility is that the valve is stretching which would also cause the clearances to close up. If that was the case something needs to be done quickly before you drop a valve.

[nhmaf]

More likely the "Valve plastic Deformation" than valve seat recession on these bikes.

You are doing the right thing to be monitoring it.
~.002" inches in about 1800 miles is indicating something may not be right, but if this is the first time that you've seen it change this much, it might be an anomaly - maybe things weren't quite the way you thought they were at the previous valve adjustment.
I'd set the clearance carefully again and check it at the same interval, or perhaps a little sooner.   If little-to-no-change, you're OK.   If it changes by .002" or more again, then you should prepare to have some headwork done.... more likely it is the exhaust valves "tuliping"  (the plastic deformation thing) because the hardened valve seats aren't carrying the heat away from the  valve well enough, and the valve head starts distorting.    The closure of the valve lash makes it appears like the valve head is wearing into the seat, but with VPD it is the head of the valve that is physically deforming due to heat.   In either case, replacing the seats and the valves is necessary.

Good luck - keep us posted!

[Barry]

It will depend on how the bikes ridden but if it helps to put it in perspective I would see no measurable change at 1800 miles and 1 or 2 thou at most over the 9000 odd miles where if I'm reading it right you measured 10 thou in total.

[mrclubike]

My bike was Mfg 11/81 and I am seeing virtually no  valve recession after 3000 miles   

[thrang]

That is way above normal levels of wear I expect to see unless your heads have a lot of miles on them, (or the soft valve seats)  and the valve train is about jiggered. If I was seeing wear like that on mine I'd deffo pull the heads and strip the valves, and have a very good look at, the push rods, valves, seats, and springs. You'll find the specs in the Haynes or Clymer manuals.  

Although I have the hardened valve seats fitted in the heads of my 81 R65, I always give the tank a squirt of lead replacement additive every second tank full.